Bore sighting device including an apertured divergent lens



L. H. BROWN April 29, 1947.

BORE SIGHTING DEVICE INCLUDING AN APERTURED DIYERGENT LENS Filed Dec.17, 1943 3H0: nap

Patented Apr. 29, 1947 UNITED STATES PATENT OFFICE BORE SIGHTING DEVICEINCLUDING AN APERTURED DIVERGENT LENS Leo H. Brown, Glenvllle, Conn.

Application December 17, 1943, Serial No. 514,614

3 Claims. (Cl. 88-1) (Granted under the act of March 3, 1883, as

amended April 30, 1928;, 370 O. G. 757) The invention described hereinmay be manufactured and used by or for the Government for gov rnmentalpurposes without the payment to me of any royalty thereon.

This invention pertains to a novel bore sight for use in connection withguns of large caliber. The operation of bore sighting is employed forthe purpose of establishing an accurate relation between the gun barreland the sighting instrument mounted upon the gun. The operation consistsessentially in aligning both the barrel and the instrument with adistant object such as a star. For practical purposes it may be assumedthat the distance ofthe object is infinite and that the two lines ofsight are therefore parallel to each other.

In this operation it is necessary, in the int erest of accuracy, tocenter the object in the muzzle of the gun. Without auxiliary aids thecentering is, however, only approximate because of the comparativelylarge image of the muzzle on the retina of the observer. The object ofthis invention is to reduce the size of this image and thereby enablethe observer to center the sighted object more accurately in the muzzleof the gun.

This object is accomplished by means of an image-reducing lens orcircular optical wedge inserted in the gun and preferably in the chamberthereof. The lens for accomplishin this function may be one that has aconcave conical surface facing the observer and a plane surface facingin the opposite direction or towards the muzzle. In the axis of the lensis an aperture through which the object is sighted directly, but ofinsuflicient size for direct sighting of the muzzle. Light from thelatter passes through the lens proper and produces a reduced image ofthe muzzle on the retina of the observers eye.

An illustrative embodiment of the invention is disclosed in thefollowing detailed description and in the accompanying drawing in which:

Figure 1 is a longitudinal section of the device, and

Figure 2 is a detail section showing also the lines of sight.

In Figure 1 is shown in cross section a gun barrel l formed at one endwith the usual chamber 2 and having a muzzle 3 at the other end. Betweenthe chamber 2 and the bore 4 is formed the usual forcing cone 5.

The bore sighting instrument of this invention includes a disk ormounting ID that is to be fitted accurately in the chamber 2 as shown inFigure l. The mounting III has a central cavity 1 I through the bottomof which is formed a comparatively small central opening l2. In thecavity and against the bottom thereof is supported a, lens [3 having aplane surface 14 lying'perpendicular to the axis of the gun and facingoutward, although it will be understood that the lens may be on eitherside of the mounting. The opposite or inward side of the lens, in theillustrated case, is a concavely conical surface [5 having its axiscoincident with the axis of the gun. The purpose of the lens, as willpresently be shown, is to reduce the image of the muzzle of the gun whensighted from the chamber 2, and any other suitable image-reducing lensmay be employed. For instance, it may be plano-concave, concave-concaveor conical-conical. The lens has a through aperture l6 considerablysmaller than the opening l 2 and centered on the gun axis which isrepresented by the dotted line H.

The reference object in the bore sighting operation, usually a star orother distant object, is

observed directly through the aperture it along the axis of the gun, theobservers eye being designated by the numeral 18 at a point somewhatbehind the chamber 2. In order that the line of sight be maintainedalong the axis H, the aperture l6 should be of a size on the order of 2to 5 mm. diameter.

The size of the opening I2 is such as to pass light rays l9 entering themuzzle 3. The aperture I6, however, is of insuflicient size to pass allof these rays, whereby a part of them are caused to pass through thebody of the optical wedge I3. The nature of the wedge is such as todiverge the rays I9, as illustrated by the refracted rays 20 proceedingfrom the optical wedge to the eye l8. Consequently the observer sees areduced virtual image of the muzzle 3, and he can therefore center thedistant object with respect to the muzzle with correspondingly greateraccuracy.

By means of the apparatus herein described, the bore sighting operationmay be performed from within a protective enclosure. The operator is notrequired to expose himself to enemy fire by going to the muzzle of thegun for mounting the cross wires in the conventional manner. Thischaracteristic of the invention is especially valuable in tank warfare.

While one specific embodiment of the invention has been shown and beendescribed, it will be understood that various alterations may be madewithout departure from the spirit of the invention as indicated by theappended claims.

What I claim is:

1. In combination with the barrel of a gun, a diverging lens mounted atthe rear end thereof auasss and adapted to form a reduced image of themuzzle, said lens having an aperture along its axis, said aperture beingcentered on the axis of said barrel. I

2. In combination with the barrel of a gun, a diverging lens mounted atthe rear end thereof and adapted to form a reduced image of the muzzle,said lens having a concavely conical surface on one side and an aperturealong its axis, said aperture being centered on the axis oi said barrel.

3. In combination with the barrel 01 agun, a mounting at the rear endthereof, a diverging lens supported by said mountin and adapted to forma reduced image of the muzzle, said lens having an aperture along itsaxis, said aperture being centered on the axis of said barrel, said -moH. BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Schumacher Nov. 1, 1938

